Can you check these sentences for me, please? Thank you.

1) The king ruled over England from 1189 to 1199. During his absence/in his absence his younger brother became king. He was unpopular because he demanded high taxes.
2) The king was orced to sign a document, accordin to which he couldn't impose taxed without the approval of a Council of advisors.
3) This document was considered (as/to be a) a forerunner of modern institutions.
4) Under Henry's reign (in his reign, during his reign, are they all possible?
5) The Parliament was established with the purpose to (of creating is possible?) create a structure of control over the king's policy.
6) The model Parliament was introduced during Edward I's reign and consisted of representatives of the Barons and the Clergy.
7) Kennings are expressions easy to remember (no: to be remembered?)
8) The Anglo-Saxons believed in an old Germanic religion and therefore, Christianity retreated (?? I need a better word) into the western part of the country.

1 - All is fine until the 3rd sentence. You need to clarify who "he" is in each instance.

2 - Check spelling of the 4th word, 9th word, 15th word; no capital on Council.

3 - should be "considered to be a..."

4 - Yes, all are possible.

5 - should be "for the purpose of creating..."

6 - OK

7 - Kennings are expressions that are easy to remember.

8 - comma after "religion" - rather than "retreated" try "moved" or even "was driven"

Sure, I can help you check these sentences!

1) The king ruled over England from 1189 to 1199. During his absence, his younger brother became king. He was unpopular because he demanded high taxes.
- This sentence looks fine. It describes the situation where the king's absence allowed his younger brother to become king, who then became unpopular due to high taxes.

2) The king was forced to sign a document, according to which he couldn't impose taxes without the approval of a Council of advisors.
- This sentence is correct. It explains that the king had to sign a document that restricted his ability to impose taxes without the council's approval.

3) This document was considered as/to be a forerunner of modern institutions.
- Both "considered as" and "considered to be" are grammatically correct. They express the idea that the document is seen as a precursor to modern institutions.

4) Under Henry's reign (in his reign, during his reign) - All three phrases are possible and convey the same idea. They can be used interchangeably to refer to the time period when Henry was king.

5) The Parliament was established with the purpose of creating a structure of control over the king's policy.
- This sentence is fine; however, "with the purpose to create" can be replaced with "with the purpose of creating" to maintain parallelism.

6) The model Parliament was introduced during Edward I's reign and consisted of representatives of the Barons and the Clergy.
- This sentence is accurate. It explains the introduction of the model Parliament during Edward I's reign and provides information about its composition.

7) Kennings are expressions easy to remember (no: to be remembered?).
- The phrasing "easy to remember" is correct. It means that kennings are expressions that can be easily remembered.

8) The Anglo-Saxons believed in an old Germanic religion, and as a result, Christianity retreated into the western part of the country.
- The term "retreated" can be used in the given context, but if you prefer a different word, you can consider replacing it with "receded" or "was confined." These alternatives would convey the idea that Christianity became less prevalent or limited to the western part of the country due to the dominance of the old Germanic religion.

I hope this helps! Let me know if you have any further questions.